It’s painfully ironic for some of the Republicans most often mentioned as possible challengers to President Barack Obama in 2012. Stances that gave them national attention and credibility are now being used as cudgels to attack them as wobbly centrists.

Minnesota’s Tim Pawlenty, for instance, gained a reputation as a pragmatic governor of a Democratic-leaning state. But now conservatives are berating him for accepting federal stimulus funds that helped him close a budget gap.

South Dakota Sen. John Thune, who also draws talk as a possible 2012 contender, said a federal bailout of banks was needed when he voted for the plan in 2008. Now, with tea party activists railing against the bailout, Thune is pushing efforts to end it.

And Mitt Romney, the closest thing to an early front-runner — and, perhaps, the establishment candidate — is struggling to explain why he expanded health care as Massachusetts governor, even as he attacks Obama’s similar plan for the nation.

Meanwhile, there’s increasing buzz about some hardline conservative Republicans who, until recently, rarely drew mention in presidential conversations. Chief among them is Texas Gov. Rick Perry. He handily defeated Sen. Kay Bailey Hutchison in last month’s Republican gubernatorial primary after positioning himself to her right on nearly every issue.

And libertarian-Republican Ron Paul bested Romney and everyone else in a straw poll of presidential favorites at February’s gathering of the Conservative Political Action Conference.

Perry and Paul are among the numerous potential candidates scheduled to speak this weekend to about 3,000 activists in New Orleans at the Southern Republican Leadership Conference.

For now, at least, the fastest-rising Republicans seem to be those most in sync with tea partiers’ aversion to taxes and Washington-based programs and regulations.